Darwin, in The Origin of Species, refers to himself as a naturalist. He also refers to or calls upon other naturalists in his introduction. The Merriam-Webster dictionary defines a naturalist as "a person who studies plants and animals as they live in nature." Funk and Wagnall's defines it as "One who is versed in natural history, as a zoologist or botanist." Most naturalist are seen as being students of botany and zoology, with a working knowledge of geology and a few other sciences. In fact, geology is somewhat necessary in defining the ecological niches that botanical and zoological specimens occupy.
Naturalist is still a highly relevant modern term for a scientist in the study of plants and animals. There currently are official State naturalists in most of the United States. The American Society of Naturalists says that their organization is "dedicated to the study of ecology, evolution, and behavior...to advance and to diffuse knowledge of organic evolution and other broad biological principles".
I think that at the present time would have been considered to Charles Darwin as a naturalist, biologist and zoologist; or Specialist in Physical and Animal Geography, which includes the identification, study, description and classification of different and new species of both plants and animals, located in their natural environment. Also, relationships and internal organization, in addition to its direct relationships or co-dependency with other species (geographic, land, rivers, lakes, vegetation and fauna)
Darwin was an Independent Scholar, a now extinct species. I think Miriam Rothschild was the last example. His inherited wealth enabled him to spread his interests far and wide and follow them wherever they led, unlike modern scientists who have to specialise narrowly and follow the herd, otherwise they will never get funding.
I always like remembering that Darwin was a fresh-faced 20-something who got lucky to be appointed as the Captain's companion on the Beagle. It makes me appreciate that people aren't born with great ideas, they develop and nurture them along with the help of colleagues and friends. Where would Darwin have been if not for Hooker or Huxley or Wallace?
If I remember correctly, Darwin's first encounter with Natural sciences was when he helped his elder brother to conduct chemistry experiments at their home. Then Darwin spent a lot of time collecting and studying insects. Chronologically, his next passion was marine invertebrates followed by geology. And all that is before he even started his famous Beagle trip. So he was truly a naturalist who embraced all the disciplines with equal passion and rigor.